1. Field of the Invention
The present invention relates to a semiconductor device such as memory or microprocessor.
2. Description of the Related Art
Conventionally, a semiconductor device such as memory and microprocessor comprises a plurality of circuits provided on a semiconductor substrate. Each of the circuits is a combination of a plurality of transistors etc. so as to carry out a certain process. Therefore, the circuits are also called function blocks.
FIG. 11 shows a plane view of an example of a conventional semiconductor device. The semiconductor device comprises a plurality of circuits 102, each of which has a specific function, mounted on, for example, a rectangular semiconductor substrate 101. The semiconductor substrate 101 includes an Input/Output region (hereinafter referred to as xe2x80x9cIO regionxe2x80x9d) 103, which is formed with a predetermined width along the outer region of the substrate 101, and a chip core region 104 surrounded by the IO region 103. The circuits 102 are mounted in the chip core region 104.
FIG. 12 shows an enlarged view of the IO region 103 and its vicinity in the semiconductor device shown in FIG. 11. The IO region 103 includes signal cells 103C for transmitting signals between each of the circuits 102 and external devices, as well as first power supply cells 103A and second power supply cells 103B for supplying electric power to each of the circuits 102. The first power supply cells 103A and the second power supply cells 103B are connected to external devices (not shown) so as to obtain a first potential (for example, a ground potential) and a second potential, respectively.
In order to distribute the electric power supplied via the first power supply cells 103A and the second power supply cells 103B throughout the semiconductor device, the IO region 103 includes a pair of ring wirings arranged around the chip core region 104, that is, a first trunk 105 and a second trunk 106. The first trunk 105 and the second trunk 106 are formed on the first power supply cells 103A, second power supply cells 103B and signal cells 103C so as to be at the same level with respect to the semiconductor substrate 101 (that is, on the same surface). The first trunk 105 and the second trunk 106 are not shown in FIG. 11.
As the first trunk 105 and the second trunk 106 are formed on the same surface, it is difficult to expand their areas, so necessary power supply cannot be obtained. Therefore, the chip core region 104 further includes another pair of ring wirings, that is, a third trunk 107 and a fourth trunk 108. The third trunk 107 and the fourth trunk 108 are connected to the first power supply cells 103A and the second power supply cells 103B, respectively, so as to have the first potential and the second potential, respectively. As shown in FIG. 11, the third trunk 107 and the fourth trunk 108 extend so as to be arranged around each of the circuits 102 in the chip core region 104, and are connected to each of the circuits 102 via branch lines 109 and 110.
However, such a conventional semiconductor device must have the third trunk 107 and the fourth trunk 108 in the chip core region 104, so it is difficult to improve the packing density of circuits 102 in the chip core region 104, which leads to an obstacle to downsizing and higher integration of the semiconductor device.
Further, as the third trunk 107 and the fourth trunk 108 must be arranged in the chip core region 104, there is a problem that the conventional semiconductor device has a low degree of flexibility in wiring design.
Moreover, as power supply paths from the first power supply cells 103A and the second power supply cells 103B to each of the circuits 102 are long, a large voltage drop occurs, which results in a deterioration in circuit characteristics.
The present invention has been achieved in light of the foregoing problems. It is an object of the invention to provide a semiconductor device capable of reducing its size, increasing its packing density, preventing a deterioration in circuit characteristics, and increasing flexibility in wiring design.
A semiconductor device according to the invention comprises a substrate including a first region and a second region having a ring shape arranged around the first region; a circuit provided in the first region of the substrate and having a predetermined function; and a power supply wiring provided in the second region of the substrate to supply electric power to the circuit, and having a laminated structure with a first power supply layer corresponding to a first potential, and a second power supply layer corresponding to a second potential.
In the semiconductor device according to the invention, as the power supply wiring of a laminated structure includes the first power supply layer and the second power supply layer, compared with a case where the first and second power supply layers are arranged on the same surface, each area of the first and second power supply layers can be expanded, so a enough supply capability of electric power can be obtained without providing additional trunks.